Piglets, for example, leave a mess (6)
I believe the answer is:
litter
I believe this clue is a double definition.
'piglets for example' is the first definition.
(group of baby animals)
'a mess' is the second definition.
(thesaurus)
'leave' is the link.
(Other definitions for litter that I've seen before include "Bits of rubbish left lying about" , "Rubbish - baby animals" , "Discarded rubbish" , "Brood of young born to an animal" , "Offspring - rubbish" .)